So, I don't have a camera yet but I'm really interested in getting into photography as a hobby (nothing professional).

I've been debating a DSLR for awhile now and have recently started liking the Nikon D3100 (good one?)

Recently though, I've been debating NOT getting a DSLR in which case I'd like to go with the Canon SX30 IS.

My question...which should I get? I'm trying to spend a little less than $300, maybe go to $400, but that'd be my max. I know the D3100 is a bit more expensive and therefore I'd have to save up more, but, do I really need a DSLR? What are the benefits in comparison to the Canon that I'm looking at?

An SLR as a first camera is overkill. You can learn an awful lot about photography, and refine your interests in the hobby, with much less expensive cameras that will not require you to spend all your time thinking about the camera at first. It is very possible that a camera like the SX30 will satisfy your needs forever. But, if you end up feeling that you need to get a more sophisticated camera sometime in the distant future, you will know what it is that you feel the need to maximize, and will make a much more informed choice of what you want to buy than you would be doing now.

There's going to be several deciding factors - budget is a big one, but not the only one.

Ask yourself what it is that you want to explore in photography. There's all sorts of sub-categories to "photography" and while a small sensor fixed lens camera can be fine for many things, it has limitations that may or may not affect what you want to do. A dSLR is the same - it's great for some things but has its limitations, too.

I don't necessarily think a dSLR would be overkill for a first camera (my husband, who knows how to turn a camera on and off and where the shutter is takes great pictures with my spare dSLR camera - all of them have an auto mode that will give good results under normal conditions). On the other hand, it can be. And it might be the wrong thing to get completely. And it's often more expensive either in the short or long run, depending on where you want to go with your photography hobby.

An expensive, feature-filled camera doesn't necessarily mean you'll take better pictures, though. That depends on whether you make the commitment to learn something about photography basics.

So there's not an absolute "right or wrong" answer to your question. More information would be needed to know if getting a dSLR right off would be the right move for you or not.

Lots of people start off with inexpensive cameras and find that they can't get the kinds of pictures they want. Lots of others are perfectly happy with them.
Many people start with SLR cameras and find them too complicated, too big, and too much trouble to carry around. Many others are willing to take the time to learn to use them effectively and are perfectly happy.
How much of a commitment do you think you will make to photography? Are you someone who really likes to dig in and learn all about a hobby, or do you expect results without doing a lot of work?
Answer these questions honestly, to yourself, and you will pretty much know what to get